1. Field of the Invention
The present invention relates to a process for separating off aminobiphenyl (ABP) from diphenylamine (DPA), which is characterized in that a substance in which oxygen is bonded by a double bond to a C atom, an N atom or another O atom is allowed to act at elevated temperature on DPA containing ABP and then the DPA is separated off.
DPA is an industrial product which, owing to its production process (Ullmann's Encyclopedia of Technical Chemistry, 4th Ed., Vol. 7, pp. 573ff; Kirk-Othmer's Encyclopedia of Chemical Technology, 4th Ed., Vol. 2, pp. 452ff) is contaminated with small amounts of ABP. The isomeric ABPs, in particular 4-ABP, have been shown to be carcinogenic and therefore must be removed as completely as possible from DPA.
2. Description of the Related Art
To remove ABP from DPA it is proposed in U.S. Pat. No. 5,107,524 to treat contaminated DPA in dissolved form with an ion exchanger. Although this procedure leads to success it is laborious and complex. Thus a prepurified DPA already freed as far as possible of coarse contaminants by distillation must be used. In addition, a solvent is required which must be removed again after the treatment. Furthermore still, the ion exchanger requires regeneration with acid after it is completely loaded with the toxic ABP. This in turn generates problems in the handling and disposal of the ABP waste liquors.
There was therefore still a requirement to provide a simple and effective process for removing ABP from DPA.